Rapidly unfolding natural or man-made disasters or emergencies such as bushfires, cyclones, and tsunamis have the potential to affect large numbers of people in a short time, with consequential risk to life and property. Such emergencies, which are often of long duration (several days), can evolve unpredictably, so that the population affected by the emergency can change at short notice. The risk to life and property is greatly reduced if people likely to be affected are made aware of the threat and informed of preventive or palliative measures (e.g. evacuation, retreat to shelters) in advance of the actual onset of the emergency.
However, people do not always gather information on an evolving emergency in the same manner. Some people may monitor a certain television station, others a certain radio station, some the Internet, and some may rely on word of mouth. In addition their monitoring may not be constant, but rather intermittent. This presents a challenge to authorities wishing to keep people informed about an emergency developing rapidly in their area of responsibility.
Known solutions including sirens and loudspeakers in public places either fail to reach many affected people or lack informative content. It is expensive and perhaps impractical to ensure wide coverage by broadcasting constant emergency update bulletins on every channel of every possible broadcast medium. Also for a potentially affected person, it can be exhausting to remain alert for updates on an evolving emergency day and night for days on end. These problems may also be exacerbated in remote or Third World regions where communications resources may be limited.
Further, emergencies affect, or have the potential to affect, different geographic areas at different times. It is wasteful and ultimately counter-productive for authorities to raise alerts concerning emergencies in areas not affected by that emergency. Therefore, some degree of selectivity by geographic area is desirable for emergency alerts.
Finally, safety-critical devices, by definition, cannot afford to fail for predictable reasons. Conventionally, self-contained emergency devices such as smoke alarms periodically test themselves for proper functioning, e.g. by sampling the battery charge level, and alert the owner if proper functioning is impaired. However, an emergency alert system can fail because of the receiver or the transmitter. It is therefore desirable for an emergency alert device to be able to monitor the transmitter for proper functioning, in addition to monitoring its own functioning.